Process of making tetrafluorohydrazine and fluorocarbons



United States Patent 3,122,416 PRQCESS OF MAKING TETRAFLUDROHYDRA- znsn AND FLUOROfiARBONS Jack R. Gould, Monsey, and Russell A. Smith, New York,

N.Y., asfignors to Staufier Chemical Company, a corporation of Delaware No Drawing. Filed May 23, 1960, Ser. No. 30,786

4 Claims. (Cl. 23-205) metal such as copper. When NF gas is passed over copper turnings at elevated temperatures, tetrafluorohydrazine can be produced; but the reaction is troublesome and unreliable since widely difierent results are obtained depending in large part upon the type of copper used, e.g., its purity, physical state, surface area, treatment prior to use in the process, etc. Results obtained with copper are unpredictable and vary between virtual nonreactivity (to give almost complete recovery of NE), and nudesirably high reactivity (to give complete conversion of the N1 and copper to elemental nitrogen and copper fluoride). In either case the yields of tetrafluorohydrazine would be low or nil. Even with the most careful preconditioning of the copper surface, the results are variable and unpredictable.

Further difficulties inherent in the copper process lie in the production of solid by-products, and in the relatively long contact times required.

It is also possible to make N F from NF by heating the N1 in a stainless steel vessel. However, even after one hour at 500 C. only a very low yield is obtained.

We have discovered a superior production process utilizing a bed of carbon as the acceptor of the fluorine from the nitrogen trifluoride. Thus, not only is N F produced but also fiuorocarbons so that the use of carbon as an acceptor is highly advantageous. Preferably, the process is conducted with a fluidized bed of carbon, although a static bed may be employed. The products of the reaction are entirely gaseous, so that the bed does not become poisoned during the course of the reaction. If a fluidized process is used, the contact of the NR with the carbon is on the order of three seconds, and the reaction is thus much faster than the prior known process utilizing copper turnings which requires contact times on the order of to minutes.

We have used various grades of carbon and it has been found that substantially any carbon may be used. The carbon produced from the coking of petroleum is inexpensive, readily available and entirely suitable. Carbon which has been activated With air and steam may be used, although such activation is not ordinarily neces .sary. The particle size of the carbon is not critical, although if a fluidized process is utilized, it is obvious that the particle size will be selected which will give ready fluidization with relatively little elutriation. In such instances, a particle size from -80 to +200 will be found suitable.

Preferably the reactor is of a material which is inert under the reaction conditions, such as stainless steel.

The reaction temperatures can vary from about 250 C. to 600 (1., preferably from 400 C. to 500 C.

As a feed gas, N1 by itself can be used, or it can be mixed with an inert gas such as helium or nitrogen although there is no particular advantage in using the inert gas. Further, the NF need not be pure, but can be a technical grade which contains contaminants, e.g. 510% CR, or low concentrations of nitrogen oxides or subfluorides.

The following non-limiting examples illustrate preferred methods of practicing the present invention. Examples 1 through 8 give data on the products of N F while Examples -9 and 10 illustrate the production of fiuorocarbons as well.

EXAMPLES 1-7 The reactor was constructed of 1 mild steel pipe threaded to accommodate hose connections at each end. The reactor was heated over a 1 foot section in a vertically supported split-level furnace. Temperatures were read from a Chromel-Alume-l thermocouple lying along the outside surface of the reactor at bed height. The reactor was loaded with an appropriate fluidizable carbon (80 +200 mesh), '3 static height, resting on a grog of 8 +20 mesh graphite lumps and placed in the furnace in a position so that the bed would fall about midway in the furnace. The bed was fluidized with helium while the temperature was being raised. A glass gas collecting train was attached to the exit end of the reactor. The-train consisted of a -l96 C. trap, preceded by a 78 C. trap, and followed by a mercury'bubbler. All connections were made with heavy wall inertplastic (Tygon) tubing. After stable operating temperature was reached, the reacting gases were admitted to the bottom of the reactor at a fluidizing flow of about0.1 ft./sec. superficial velocity. Flow rates were measured with flow meters. When the reaction was finished, the apparatus was swept out with helium and the contents of the 196 C. trap taken to the vacuum line for examination. The following data were obtained:

Table THE PREPARATION OF N2F4 BY THE REACTION OF NFa WITH A FLUID BED OF CARBON Feed Recovery Percent Example Type Rate, Temp, Mols (moles) Percent Percent Yield Number Coke Feed Gas 00.] C. N F; Conv. Yield N211 Min. Fed N F3 N213; (Cor- NFs N2F4 rested) A 2NF321 He-. 270 450 0. 18 0. 135 0.021 25 23 93 A 2NF3:1 He 270 470 0.185 0.11 0.031 40. 5 33. 5 84 A N 250 470 0. 19 0.052 0. 030 73 31. 5 42 A 302 440 0. 12 0. 029 0. 033 76 73 B 302 400 0. 12 0. 036 0.011 18 26 B 320 360 0. 13 0. 102 0.009 21. 5 14 69 A 280 490 0.225 0. 049 0. 068 78 60 77 Coke A: National Carbon Co. petroleum coke W-8300, SO +200 mesh aerated for removal of fines. Coke B: Petroleum coke, activated in two stages with air and steam, 80 +200 mesh, aerated for removal 3 EXAMPLE 8 In order to demonstrate the use of a static bed in carrying out the reaction, the reactor and auxiliary equipment described was used except that the coke was etroleum coke sized 8 +20 mesh. The feed gas was N1 fed at a rate of 320 cc. per minute and the temperature was maintained at 400 C. A quantity of 0.12 moles of NE; was fed and there was recovered 0.09 moles NF and 0.01 moles N F This represents an NF conversion of 25%, a yield of 17% N F and a corrected yield of 67% N F EXAMPLE 9 Nitrogen trifluoride was passed at the rate of 0.1 linear ft./sec. through a 1-inch tubular steel reactor containing a 3-inch bed of 65-150 mesh fiuidizable carbon. The outside wall temperature of the reactor was 440 C. The exit gases were trapped in a collection train consisting of a 7 8 trap followed by a -l96 trap. The contents of the -l96 trap were analyzed by fractional condensation, and by infrared analysis. Tetrafiuorohydrazine and fiuorocarbons were produced according to the following:

Introduced Obtained 0.029 mole NFa. 0.022 mole CF4. 0.033 mole N2F4. 0.006 mole CzFa.

0.121 mole NF; (contained 0.014 mole CF; as

contaminant) Introduced Recovered 0.049 mole NFa. 0.040 mole CF4. 0.068 mole N2F4. 0.014 mole OzFo.

0.225 mole NFa (containing 0.025 mole CF; as

contaminant) Consequently, 78% of the N1 was converted and of this, 77% appeared as N F Carbon tetrafiuoride, 0.015 mole, and 0.014 mole of C 1 were created by reaction with the carbon. This represents 34.1% yield of CE; and 48.3% yield of C 1 in accordance with Equations 1 and 2.

This application is a continuation-in-part of application Serial No. 803,801, filed on April 2, 1959.

We claim:

1. A process of making N 11 and fiuorocarbons consisting of heating a gas selected from the class consisting of NE, and an NF -inert gas mixture to at least about 250 C. and not in excess of about 600 C. while in contact with a bed of carbon.

2. A process of making N F and fluorocarbons consisting of heating a gas selected from the class consisting of N1 and an NF -inert gas mixture to at least about 250 C. and not in excess of about 600 C. while in contact with a bed of fluidized particulate carbon, said carbon being obtained from the coking of petroleum.

3. A process of making N 11; and fluorocarbons consis-ting of heating a gas selected from the class consisting of N1 and an NF -inert gas mixture to at least about 250 C. and not in excess of about 600 C. while in contact with a bed of fluidized carbon particles, said carbon falling within the particle size range -80 to +200 mesh, said carbon being obtained from the coking of petroleum.

4. A process of making N F and fiuorocarbons consisting of heating a gas selected from the class consisting of NF and an NF -inert gas mixture to at least about 400 C. and not in excess of about 500 C. While in contact with a bed of fluidized carbon particles, said carbon falling within the particle size range -80 to +200 mesh, said carbon being obtained from the coking of petroleum.

References Cited in the file of this patent UNITED STATES PATENTS 2,709,186 Farlow et al May 24, 1955 OTHER REFERENCES Colburn et al.: Journal of The American Chemical Society, vol. 80, page 5004 (September 1958). (Copy in Denison et a1 Sept. 16, 1958 

1. A PROCESS OF MAKING N2F4 AND FLUOROCARBONS CONSISTING OF HEATING A GAS SELECTED FROM THE CLASS CONSISTING OF NF3 AND AN NF3-INERT GAS MIXTURE TO AT LEAST ABOUT 250*C. AND NOT IN EXCESS OF ABOUT 600*C. WHILE IN CONTACT WITH A BED OF CARBON. 